1. Field of the Invention
The present invention generally relates to the field of screen recorders, and more specifically to a method for specifying a video window's boundary coordinates to separate the video signal into high and low variance components and compress the respective components.
2. Description of the Related Art
Conventional color televisions and display monitors produce relatively low resolution and bandwidth red, green and blue (RGB) video signals, e.g. 400-600 lines per frame at 25-30 frames per second, that conform to one of several international standards. Three of the most common standards are: the National Television Systems Committee (NTSC) standard with 525 lines per frame at 30 frames per second, the Sequential Chrominance Signal & Memory (SECAM) standard with 625 lines per frame at 25 frames per second and the Phase Alternating Line (PAL) standard with 625 lines per frame at 25 frames per second. These standards are fairly flexible in that the number of scan lines actually used by a display may be significantly less than the specified standard. For these low resolution signals, video recording devices, such as video cassette recorders (VCRs), record the analog signal directly onto a magnetic tape.
For high resolution workstation monitors having 1280 or greater scan lines per frame, or high definition television (HDTV), it is not currently feasible to record the analog video signals directly onto the tape in an analog format at the same high resolution. The storage requirements and bandwidth of the video signals exceed the capabilities of analog recording devices. For example, a 1280.times.1024 video signal at 3 bytes per pixel and 30 frames per second recorded for 3 hours would require 1274 Gbytes of memory and a bandwidth of 943 Mbps. As a result, in a current approach a scan converter is used to convert the high resolution video signal into one of the low resolution standard formats, which is recorded onto the tape. The down conversion is done by averaging adjacent scan lines or simply skipping scan lines, and results in a substantial loss of resolution when the recorded tapes are played back. The "RGB/Videolink 1600U" RGB Spectrum of Berkeley, Calif., 1991 is described in a product bulletin as one example of a scan converter. The loss of resolution is particularly bothersome in a multimedia workstation, a typical display includes text, graphics, pictures, audio and motion picture video data. The graphic icons and text are distorted by converting the high resolution signal to the relatively coarse low resolution signal. This system sacrifices image quality to maintain manageable storage requirements and bandwidth. For applications where the replayed information is required to faithfully reconstruct events, e.g., air traffic control displays, or is critical to litigation, the loss of fidelity may make the recording unuseable.